We have developed and characterized a cell line, K-562, originally derived from a patient with chronic myelogenous leukemia (CML). This cell line has the Philadelphia (Ph1) chromosome and is free of Epstein-Barr virus genome, herpes-like virus, mycoplasma, and does not have T or B cell markers. Such a cell line not only provides a controlled and uniform source of ML cells free of some common oncogenic viruses, but also can be examined for relative synthesis of specific antigen with respect to karyotype. These ML cells when injected into rabbits or monkeys cause the production of specific antibodies that show complement mediated cytotoxicity for the K-562 cell line and ML cells from patients. This cytotoxicity is not removed if the serum is absorbed with leukocytes or granulocytes from normal donors. Absorption with ML cells or K-562 cell line does effectively remove the cytotoxic activity. The antisera are not cytotoxic for normal human leukocytes. The purpose of this project is: (1) to evaluate further the specificity of the antisera and their use as diagnostic and/or prognostic tools; (2) to isolate and characterize the ML specific antigen(s) from the K-562 cell line; and (3) to characterize the antibody produced during the immune response at selected intervals and assess the cytotoxicity on cells from normal individuals and patients suffering from leukemias, lymphomas, and other hematologic and non-hematologic diseases.